Dear Flipbook <= 2.4.30 - Authenticated (Contributor+) Stored Cross-Site Scripting via '.df-element' Element Inner HTML

The Dear Flipbook – PDF Flipbook, 3D Flipbook, PDF embed, PDF viewer plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'post_content (Custom HTML block inner HTML)' parameter in all versions up to, and including, 2.4.30 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. A Contributor-level attacker can insert a crafted .df-element div with data-df-lightbox='thumb' via a Custom HTML block, whose inner HTML is passed as the title argument to parseThumbs() at render time, enabling both innerHTML injection into a span element and attribute breakout via an onerror handler on a constructed img element.